1. Statement of the Technical Field
The invention concerns a method for filtering particles from a fluid. More particularly, the method concerns a method for filtering particles of two or more size ranges, and having different relative concentrations.
2. Description of the Related Art
A filter typically consists of a cartridge or bag for use in a pressurized filter system. A pressurized filter system utilizing filter bags is typically comprised of a filter housing having a body and a cover. The body contains a filter basket for placing the filter bag therein. The filter housing is comprised of a mounting stand, an input orifice and an output orifice. A contaminated fluid is pumped into the filter housing through the input orifice. The contaminated fluid contains one or more types of particles to be filtered (PTBFs). Each type of PTBF has a different particle size. The contaminated fluid also contains different concentrations of each PTBF type. The PTBFs are filtered from the contaminated fluid as the fluid flows through the filter bag and then exists through the output orifice. Such a pressurized filter system is disclosed in U.S. Pat. No. 5,246,581.
Fluids to be filtered often contain various types of particles which are to be removed by the filtering operation. For example, a first type of particles may have a first range of particle sizes, whereas a second type of particulate may have a second range of particle sizes. Filtration apparatus such as filter bags or filter cartridges can be specially designed for these types of filtering operations. A filter bag or cartridge can often include a first type of filter material intended to filter the first type of particle, and a second type filter material intended to filter the second type of particle. For example, the first filter material can be designed to capture relatively large particles of the first type whereas the second filter material can be selected to capture relatively smaller particles of the second type. The first and second filter materials are commonly arranged in layers through which the fluid is passed. These arrangements can be quite effective for efficiently filtering the two different particle types.
Still, there are problems which tend to arise when attempting to filter various different types of particles contained in a fluid. For example, the concentration of the various different types of particles may be different. The concentration of the first type of particle within the fluid can be much higher as compared to the second type of particle. Stated differently, the two or more particle streams have different percentages of concentration and different weights. Alternatively, the concentration of the second type of particle might be much higher as compared to the first type of particle. Over time, this difference in particle concentration will generally result in a larger quantity of one particle type or the other being collected in the filter.
Significantly, each filter material will have a limited capacity or capability to capture particulate matter. After this capacity is reached, the filter can become so heavily laden with filtered particulate matter that the flow rate of fluid through the filter material is substantially diminished. This condition is sometimes referred to as blinding. When a first type of particle is captured in a first filter material layer and a second type of particle is captured in a second filter material layer, one filter material layer may become blinded before the other. For example, a concentration of a first particle type can be ten times higher as compared to a second particle type. In such cases, a first filter material for capturing the first particle type might become blinded at a rate that is ten times faster as compared to a second filter material for capturing a second particle type. Notably, the filter bag or cartridge must be replaced once any of the filter materials layers becomes blinded, even if other filter materials comprising the filter bag or cartridge still have additional capacity. This is due to the fact that the filter material layers are arranged serially. If one layer is clogged with particles, the other layers will no longer function effectively.
The foregoing problem can result in a shortened life cycle for a filter bag or cartridge. A single layer of filter material, once clogged, can effectively require replacement of the entire filter bag. Accordingly, there is a need for an improved filter bag in which the life of filter mediums provided for particles having different types and concentrations is more effectively equalized.